The present invention relates to a vehicle air conditioning apparatus for regulating temperature circumferences in a vehicle compartment.
In general, various attempts have heretofore been made to provide a vehicle air conditioning apparatus, for regulating temperature circumference in a vehicle compartment, that includes a refrigeration cycle operative to achieve heat exchange between refrigerant and air by circulating refrigerant, and a hot water line operative to achieve heat exchange between engine coolant and air by circulating engine coolant which is heated by waste heat of an engine.
With such an air conditioning apparatus, an inside-vehicle-compartment air flow passage into which inner and outer air streams are introduced is provided with an evaporator, that serves as a heat-absorbing inside-vehicle-compartment heat exchanger adapted to be incorporated in the refrigeration cycle, and a heater core serving as a heat radiator adapted to be incorporated in the hot water line.
Compelling heat of the air stream passing through the inside-vehicle-compartment air flow passage to be absorbed by refrigerant in the evaporator forms cold wind, whereas the air stream passing through the inside-vehicle-compartment air flow passage is heated by the heater core to form how wind. Then, regulating mixture ration between these cold wind and hot wind by means of an air mixing door allows the temperature in the vehicle compartment to be adjusted.
Also, refrigerant, that is evaporated upon absorption of heat in the evaporator, is then compressed by the compressor adapted to be driven by the engine and discharged to the main condenser, serving as an outside-vehicle-compartment heat exchanger, where heat of refrigerant is radiated and condensed whereupon refrigerant is expanded by an expansion valve, serving as an expansion valve, and subsequently delivered into the evaporator.
During such an air conditioning cycle, since the vehicle air conditioning apparatus is arranged to form hot wind by means of heating medium composed of engine coolant, under a circumstance where the temperature of engine coolant is not very high, such as a situation just after startup of the engine or a situation where a traveling load remains at a low level, an issue is encountered in that it becomes hard to rapidly raise the temperature in the vehicle compartment.
In view of such an issue, vehicle air conditioning apparatuses, disclosed Japanese Patent Application Laid-Open No. 9-175140 and Japanese Patent Application Laid-Open No. 10-44742, have inside-vehicle-compartment air flow passages each of which incorporates a sub condenser, serving as a heat-radiating inside-vehicle-compartment heat exchanger, whereby during a heating mode, refrigerant detours a main condenser to circulate through the sub condenser, an expansion valve, an evaporator and a compressor to cause heat of refrigerant in the sub condenser to be heat radiated to an air stream passing through the inside-vehicle-compartment air flow passage.
With the vehicle air conditioning apparatus with such a structure, since hot wind is generated not only by the heater core heated by heating medium composed of engine coolant but also by the sub condenser heated by heating medium composed of refrigerant, the temperature in the vehicle compartment can be raised at an increased level in a relatively short period.
Further, if a heating means is provided to heat the sub condenser, the temperature load of the sub condenser can be raised and this enables a discharge refrigerant pressure to be rapidly raised, with a resultant capability of raising the temperature in the vehicle compartment in a further rapid manner.
Also, with the air conditioning apparatus of this type, for the purpose of saving drive power, an attempt has been made to turn off a compressor clutch, serving as a coupling and uncoupling means, to disconnect the compressor from the engine at a timing when the vehicle compartment reaches a preset temperature, thereby shifting the heating mode to be achieved only by the heater core.
However, with the related art air conditioning apparatus of this type, an issue is encountered in an inability to stabilize the blow-off temperature because of probabilities where the discharge pressure of refrigerant gas discharged from the compressor at a high pressure varies in dependence on variations in load (an intake air temperature and a volume of hot wind) of the evaporator and rotational speed of the engine and where the compressor is forced to be interrupted to restrict an increase in pressure at the high pressure side for the purpose of precluding the evaporator from freezing or to protect the compressor or the refrigeration cycle.
Further, in recent years, due to improvements over the engines to operate at high efficiencies, the engine tends to provide a decreased amount of exhaust heat and, therefore, if the compressor clutch is turned off to cause the heating to be achieved only by the heater core, the blow-off temperature rapidly drops, resulting in an issue to cause a vehicle occupant to have a sense of incompatibility.
To address such an issue, although it is conceivable to use a method in which the temperature is adjusted by regulating the opening degree of an air mixing door with the compressor clutch remaining turned on, such a method undergoes another issue in reduction in power savings arising from a prolonged length of time in which the compressor is driven.
The present invention has been completed with the above issues in mind and has an object of the present invention to provide a vehicle air conditioning apparatus in which a compressor is continuously operated while contemplating to protect the compressor and a refrigeration cycle and to prevent a heat-absorbing vehicle-compartment-inward heat exchanger from freezing for thereby enabling a blow-off temperature to be stabilized while realizing power savings with an improved comfortability.
To achieve the above object, a first aspect of the present invention provides a vehicle air conditioning apparatus comprising a heat-radiating inside-vehicle-compartment heat exchanger adapted to radiate heat of compressed gas-phase refrigerant into an air stream to be blown off to a vehicle compartment for condensing refrigerant, expansion means for expanding the refrigerant condensed in the heat-radiating inside-vehicle-compartment heat exchanger, heat-absorbing inside-vehicle-compartment heat exchanger adapted to compel heat of the air stream inside the vehicle compartment to be absorbed by the refrigerant expanded by the expansion means, a variable displacement compressor adapted to be driven by an engine to compress the refrigerant evaporated in the heat-absorbing inside-vehicle-compartment heat exchanger, blow-off temperature detection means for detecting a blow-off temperature or a numeric value correlated with the blow-off temperature, and compressor control means operative to control a discharge refrigerant volume of the variable displacement compressor such that the blow-off temperature lies at a given temperature responsive to a detection result of the blow-off temperature detection means.
A second aspect of the present invention relates to a vehicle air conditioning apparatus of the first aspect and further comprises intake refrigerant pressure detection means for detecting an intake refrigerant pressure of the variable displacement compressor or a numeric value correlated with the intake refrigerant pressure, wherein the compressor control means controls a discharge refrigerant volume of the variable displacement compressor such that, in response to a detection result of the intake refrigerant pressure detection means in addition to the detection result of the blow-off temperature detection means, the blow-off temperature becomes closer to a given temperature while maintaining a compression ratio of the variable displacement compressor at a value below a given value.
A third aspect of the present invention relates to a vehicle air conditioning apparatus of the first aspect and further comprises outer and air regulator means for regulating a ratio between an inner air stream and an outer air stream to be introduced into an inside-vehicle-compartment air flow passage, an outlet temperature detection means for detecting an air temperature at an outlet of the heat-absorbing inside-vehicle-compartment heat exchanger or a numeric value correlated with the air temperature, and inner and outer air control means responsive to a detection result of the outlet temperature detection means to control the inner and outer air regulating means such that an air temperature at an outlet of the heat-absorbing inside-vehicle-compartment heat exchanger lies at a given value.
A fourth aspect of the present invention relates to a vehicle air conditioning apparatus of the first aspect and further comprises inner and outer air regulating means that regulates a ratio between inner and outer air streams to be introduced into the inside-vehicle-compartment air flow passage, heating temperature detection means that detects a heating temperature of the heating means or a numeric value correlated with the heating temperature, inlet temperature detection means that detects an air temperature at an inlet of the heat-absorbing inside-vehicle-compartment heat exchanger or a numeric value correlated with the air temperature, and inner and outer air control means operative to calculate a target air temperature at an inlet of the heat-absorbing inside-vehicle-compartment heat exchanger for causing an air temperature at an outlet of the heat-absorbing inside-vehicle-compartment heat exchanger to lie at a given temperature in response to a detection result of the heating temperature detection means while controlling the inner and outer air regulating means for causing an air temperature at an inlet of the heat-absorbing inside-vehicle-compartment heat exchanger to lie at the target air temperature in response to a detection result of the inlet air temperature detection means.